Generally, a construction machine, such as a hydraulic excavator, is provided at an upper portion of a travel base, with a revolving frame interposed therebetween, and is equipped with: a revolving upperstructure that revolves horizontally; and a front working mechanism that is mounted forward of the revolving upperstructure so as to turn vertically. The revolving upperstructure has: an engine that is stored in an engine room; a main pump that is driven by the engine; and a control valve that controls the flow of the hydraulic oil discharged from the main pump.
Meanwhile, the front working mechanism has: an actuator that operates with the hydraulic oil supplied from the control valve; and a work body that is driven by the actuator, and work, such as drilling, is performed by the work body. At this time, the engine is driven, and the hydraulic oil is discharged as hydraulic fluid to the actuator from the main pump through the control valve, thereby causing a gradual increase in the temperature of engine cooling water and hydraulic oil.
In order to suppress such increase in the temperature of engine cooling water and hydraulic oil, there are provided within the revolving upperstructure a radiator for cooling engine cooling water, an oil cooler for cooling the hydraulic oil discharged from the main pump, and a cooling fan for cooling with cooling air generated by its rotation the engine cooling water and hydraulic oil circulating in the radiator and the oil cooler.
Furthermore, the construction machine is provided with a cooling fan control device so as to provide the most suitable cooling efficiency for various conditions and environments in the revolving upperstructure, the cooling fan control device being capable of adjusting the flow rate of the cooling air by controlling the rotational speed of the cooling fan. As one of such known cooling fan control devices, there has been proposed a control device for a hydraulically-driven cooling fan (for example, see Patent Literature 1), which is applied to a cooling fan provided independently from the engine and is equipped with: a detection unit that detects a state quantity, to be described later, associated with the driving of the cooling fan; and a control unit that controls the rotational speed of the cooling fan on the basis of the state quantity detected by the detection unit.
More specifically, in the related-art control device for the hydraulically-driven cooling fan, engine cooling water temperature, hydraulic oil temperature, and engine rotational speed are used as the state quantity associated with the driving of the cooling fan. The control unit stores data on a target fan rotational speed corresponding to each of the engine cooling water temperature, the hydraulic oil temperature, and the engine rotational speed, and makes comparisons between the target fan rotational speed corresponding to the detected engine cooling temperature and the target fan rotational speed corresponding to the detected hydraulic oil temperature to select the higher target fan rotational speed, and then makes comparisons between the selected target fan rotational speed and the target fan rotational speed corresponding to the detected engine rotational speed so as to control the rotational speed of the cooling fan in accordance with the lower target fan rotational speed. Furthermore, an upper limit to the cooling fan rotational speed is set in accordance with the engine cooling water temperature and the hydraulic oil temperature.
Therefore, in the case where the above-described related-art control device for the hydraulically-driven cooling fan is applied to a hydraulic excavator, upon changes in engine load due to work, such as drilling, the cooling fan is controlled to a fixed rotational speed in accordance with engine cooling temperature and hydraulic oil temperature, and thus insufficient cooling or overcooling by the cooling fan can be suppressed. If work is conducted by a hydraulic excavator in an environment, such as a cold climate area, where engine cooling water temperature and hydraulic oil temperature are likely to decrease, on the other hand, the warm-up operation, such as bucket crowd relief, in which the bucket is moved in the crowding direction to increase the load on the main pump, is performed in order to quickly increase the engine cooling water temperature and the hydraulic oil temperature and bring the operation of the vehicle body in good condition.